1. Field of the Invention
The present invention relates to a choke valve for an automatic transmission provided within a valve body interposed between two separator plates.
2. Description of the Related Art
An automatic transmission includes hydraulic units such as a hydraulic clutch, a hydraulic brake and a torque converter. Various types of valves that control the operation of these units are each housed within a valve body on either face of which a separator plate is superimposed. By superimposing the separator plates on the opposite faces of the valve body in this way, it is possible to form oil passages between the separator plates and oil channels that are formed on the surface of the valve body. Such a hydraulic control system of an automatic transmission has a choke valve for controlling the flow rate of the oil according to the temperature conditions, as disclosed in Japanese Patent Application Laid-open No. 63-186058.
As shown in FIG. 7, a conventional choke valve 02 provided within a valve body 01 includes a valve hole 03 that opens on an end face of the plate-shaped valve body 01, a valve main body 04 that is fitted in the valve hole 03, and a clip 05 that prevents the valve main body 04 from falling out. Formed in the valve hole 03 are an inlet port 03a, an outlet port 03b and an air release port 03c. The valve main body 04 has a clip channel 04a with which the clip 05 engages and a small diameter section 04b. Formed between the inner periphery of the valve hole 03 and the outer periphery of the small diameter section 04b of the valve main body 04 is an annular choke 06. The inlet port 03a and the outlet port 03b communicate with each other via the choke 06.
With regard to the conventional choke valve 02 shown in FIG. 7, because it is necessary to machine out the inner periphery of the valve hole 03 so as to form the inlet port 03a and the outlet port 03b, the number of machining steps increases. Furthermore, because it is necessary to employ the clip 05 in order to prevent the valve main body 04 from falling out, the number of parts increases.
The present invention has been carried out in view of the above-mentioned circumstances and it is an object of the present invention to reduce the cost by simplifying the structure of a choke valve for an automatic transmission.
In order to achieve the above-mentioned object, there is proposed a choke valve for an automatic transmission provided within a valve body interposed between two separator plates, wherein the choke valve is formed from a valve hole having a circular cross-section that runs through the valve body in its thickness direction and a columnar valve main body that is fitted in the valve hole, the valve main body having a pair of annular channels formed on the outer periphery of the valve main body at opposite ends and a small diameter section formed between the two annular channels, the small diameter section together with the valve hole forming a choke, and a pair of ports formed between the two separator plates and oil channels formed on opposite faces of the valve body communicate with the pair of annular channels, respectively.
In accordance with the above-mentioned arrangement, because the valve main body is fitted in the valve hole that runs through the valve body in its thickness direction and the valve main body is prevented from falling out by utilizing the separator plates that are superimposed on the valve body, it is unnecessary to employ special means such as a clip to prevent the valve main body from falling out, thus contributing to a reduction in the number of parts and the number of assembly steps. Moreover, because the pair of ports are formed between the two separator plates and the oil channels formed on the opposite faces of the valve body, it is unnecessary to make channels on the inner periphery of the valve hole so as to form the ports, thus reducing the number of machining steps and achieving a reduction in cost.
Furthermore, there is proposed a choke valve for an automatic transmission wherein the valve main body is retained by a step formed on one end of the valve hole.
In accordance with the above-mentioned arrangement, retaining the valve main body by means of the step at one end of the valve hole can prevent the valve main body from falling out when it is provisionally assembled in the valve hole, thus making assembly of the separator plates easy.